When selecting hardware for Exchange 2010, we recommend that you consider the server maximum memory configuration. Different server architectures have different memory limits. We recommend that you check the following technical specifications of the server to determine the most cost-efficient maximum memory configuration for your servers:

Memory speed Some server architectures require slower memory modules to scale to the maximum supported amount of memory in a specific server. For example, maximum server memory could be limited to 32 GB with PC3 10666 (DDR3 1333) or 128 GB using PC2 6400 (DDR2 800). You should check with the manufacturer to ensure that the memory configuration target for Exchange 2010 is compatible in terms of speed.

Memory module size Consider the largest memory module size that the server will support. Generally, the larger the memory module, the more expensive. For example, two 2 GB DDR SDRAM memory modules generally cost much less than one 4GB DDR SDRAM memory module and two 4 GB DDR SDRAM memory modules generally cost much less than one 8GB DDR SDRAM memory module. Make sure the maximum memory module size allows you to meet your target memory requirements for Exchange 2010.

Total number of memory slots Consider how many memory modules that a specific server will support. The total number of slots multiplied by the maximum memory module size provides the maximum memory configuration for the server. Keep in mind that memory modules must sometimes be installed in pairs.

Be aware that some servers experience a performance improvement when more memory slots are filled, while others experience a reduction in performance. Check with your hardware vendor to understand this effect on your server architecture.

After the number of processor cores estimated to be required per server role is understood, baseline memory recommendations can be applied. The following table illustrates the minimum supported and recommended memory configurations for Exchange 2010 server roles.

The following describes the minimum requirements and recommended maximum configurations:

Minimum Supported This is the minimum memory configuration suitable for Exchange 2010 servers. The minimum hardware requirements must be met to receive support from Microsoft Customer Service and Support.

Recommended Maximum This is the recommended memory configuration for specific server roles. Recommended maximum is defined as the upper limit of viable processor and memory configurations based on price and performance. The recommended maximum configuration is a guideline. It isn't a support criterion, and it doesn't take into account the resource requirements of third-party applications that might access or be installed on the server. The recommended maximum configuration may change over time based on price changes and technology advancements.

The following table shows the minimum supported and recommended maximum memory configurations for Exchange 2010.

The Edge Transport and Hub Transport server roles don't require substantial quantities of memory to perform well in optimal conditions. Generally, 1 GB of RAM per processor core (4 GB minimum total) is sufficient to handle all but the most demanding loads. Most deployments will be optimally configured with the recommended memory configuration of 1 GB per processor core (4 GB minimum total).

In general, memory utilization on Client Access servers has a linear relationship with the number of client connections and the transaction rate. Based on the current recommendations of 2 GB per core processor and memory configurations, a Client Access server will be balanced in terms of memory and processor utilization, and it will become processor-bound at approximately the same time it becomes memory- bound.

These recommendations are based on the Exchange 2010 feature, RPC Client Access. This feature requires a larger memory and processor configuration to manage the increased loads placed on the Client Access server role.

The memory configuration process for the Mailbox server role is more complex than the other roles because the optimal memory configuration depends upon the server roles installed, the mailbox count, the client profile (similar to estimating processor core requirements), and the number of active databases.

Memory sizing for the Mailbox server role is critical to reducing disk input/output (I/O) on the server. The more memory you add to the Mailbox server, the less disk I/O will be generated by Exchange. There is, however, a point of diminishing returns at which adding memory to the server may not be justifiable based on price and performance. The recommendations discussed in "Recommended Memory Configurations" earlier in this topic consider this point of diminishing returns and are based on current memory prices and performance metrics.

For more information about how to perform appropriate memory sizing for the Mailbox server role, see the following topics:

When determining memory requirements for multiple role server configurations, you need to consider the requirements of Hub Transport, Client Access, and Mailbox server roles. To assist you, we have provided the calculated memory requirements in the preceding table. For additional information, see the following: